Add Index for Instances Full-text Subjects Search

Overview:
Currently doing an Instance subject search by any keyword in an environment that has over 1.5 million instances records takes more than 80 seconds to return. mod-inventory-storage log shows a warning for missing full-text index. When applying a subjects full text index to the {tenant}_mod_inventory_storage.instance table the response time improved dramatically to under 2 seconds.

Steps to Reproduce:

• Navigate to Inventory app
• On the left "Search & Filter", make sure "Instance" is selected
• Click on the first drop down to select "Subject" search option
• Enter a keyword to search.
• * Note that in a database with more than 1 million records it will take more than a minute for results to return.

*Expected Results: *UI should return results within 2 seconds
Actual Results: takes more than ~1 minute

Interested parties:
Customers, everyone.

Acceptance criteria:
1. mod-inventory-storage db_scripts/schema.json is updated with the subjects full text index on instances table,
2. the subjects ginIndex is deleted from schema.json.